1. Field of the Invention
The present invention relates to a dielectric ceramic composition and electronic device wherein said dielectric ceramic composition is applied to its dielectric layer. More precisely, the present invention relates to a dielectric ceramic composition having good characteristics under a high electric field intensity, and to an electronic device wherein said dielectric ceramic composition is applied to dielectric layer and its internal electrode is mainly composed of a base metal.
2. Description of the Related Art
In recent years, a demand for a high reliability of electronic device is high. For instance, size reduction and high performance of multilayer ceramic capacitor, an example of electronic device, is rapidly processing; while its use is expanding. As a result, various characteristics are required for such capacitors.
Conventionally, ceramic composition showing ferroelectricity (ferroelectrics), such as barium titanate, is often used for dielectric layer of electronic device, such as capacitor.
However, when electronic device having dielectric layer of ferroelectrics is used under a high rated voltage, namely, when it is used under a high field intensity, various problems due to ferroelectricity of the ceramic composition were caused.
For instance, there was a problem that specific permittivity rapidly decreases as field intensity increases; and as a result, effective capacitance under used environment decreases. In addition, there were problems that capacitance of capacitor decreases as specific permittivity of dielectrics decreases, which leads to deterioration of DC-Bias characteristic, and cracks or noises due to electrostriction generate. There was also a problem such as a deterioration of capacitance change rate with respect to temperature.
Therefore, dielectric ceramic composition having good characteristics (such as specific permittivity) is required, even when field intensity is high (e.g. superimposed direct current).
Further, one way to manufacture electronic device at a low cost is to use base metal as electrode material. In particular, when base metal is used for material of internal electrode of multilayer electronic device, dielectric layer and internal electrode are required to be cofired under a reduced atmosphere. Thus, ceramic composition, composing dielectric layer cofired with the base metal, is required to show resistance to reduction.
The below descried Article 1 describes a compound wherein rare-earth element is solid solved in BaNb2O6 having tungsten bronze-type structure.    [Article 1] Kunio Masuno, “X-Ray and Dielectric Studies of the Systems (Ba1-xR2x/3)Nb2O6, Where R is Y, Sm or La”, Journal of the Physical Society of Japan, 1964, Vol. 19, No. 3, p. 323-328